Venturi tubes are well known in the art for introducing a second fluid into a first fluid. Typically, the inlet of the venturi tube is attached to a conduit for the first fluid, and the second fluid is introduced through a second inlet, hereafter called an aspirator inlet, so that the combined fluid exits through the venturi's outlet. In operation, the gas or liquid to be introduced is sucked into the venturi through the aspirator inlet, as the fluid flows through the venturi tube. For a given venturi tube, the aspiration rate depends on the flow rate of the fluid which passes through the venturi inlet and the viscosity of the fluids.
One of the major problems associated with conventional venturi tubes is that any single tube can only operate over a narrow range of fluid flow rates. This is in part because back pressure produced within the venturi increases greatly with increases in the fluid flow rate. It is known that this problem can be overcome by connecting an external bypass system to the fluid conduit, in parallel to a venturi tube, so that a portion of the fluid flow stream flowing through the conduit bypasses the venturi by flowing through the bypass system. Conventional bypass systems have several limitations including being costly, bulky and requiring complex plumbing which hinders easy installation in association with an existing fluid conduit.
There exists a need for a simple venturi tube apparatus which can be added easily to an existing fluid carrying conduit and which can operate over a wider range of fluid flow conditions.